Pocket Guide to Stress Testing

Dennis A. Tighe, Bryon A. Gentile, Dennis A. Tighe, Bryon A. Gentile

• Editorial: Wiley-Blackwell
• Año: 2019
• ISBN:
  9781119481751
• Edición: 2
• Categoría: Medicine
• Categoría: Cardiology

The go-to handbook for those performing and analysing cardiac stress tests

The stress test is key to the clinical evaluation and management of patients with known or potential cardiovascular disease. By measuring the heart's ability to respond to external stress, it can provide vital insights into the general physical condition of patients, highlighting abnormalities in blood flow, risk of coronary artery disease, and more. The Pocket Guide to Stress Testing gives cardiology professionals a complete breakdown of this everyday procedure that they can carry with them and consult on the go.

This second edition has been fully revised to reflect the most up-to-date information available on the best approaches to conducting and interpreting various forms of stress test. With chapters spanning topics such as testing guidelines, nuclear imaging techniques, and emergency and aftercare protocols, the clear and practical contents cover all aspects of the subject. This essential new text includes:

• A complete overview of exercise stress testing, covering indications, protocols, preparation, and interpretation
• Guidelines for the standard treadmill test, as well as for the various pharmacological stress tests for patients unable to complete an exercise ECG test
• An extensive list of references and reading suggestions to help trainees to expand their knowledge
• End-of-chapter summaries and new tables and illustrations

As the field of cardiology continues to change and develop apace, this new edition of The Pocket Guide to Stress Testing provides physicians, trainee cardiologists, and cardiac nurses with a reliable, up-to-date resource for use in everyday practice.

1
Introduction

Dennis A. Tighe

Introduction

The stress (exercise) ECG test serves as an important and valuable assessment tool that provides diagnostic and prognostic information in the clinical evaluation and management of patients with known or suspected cardiovascular disease, particularly coronary artery disease (CAD).

Various protocols for exercise stress testing have been in in existence for several decades. Early protocols for exercise testing, such as Master’s two‐step test, lacked sufficient sensitivity for clinical use. Currently in the United States, exercise electrocardiography is most commonly performed using a motor‐driven treadmill. In Europe, where bicycling is more habitual, exercise stress testing is more commonly performed using a bicycle ergometer. Several multistage exercise ECG testing protocols have been developed for use with either a motorized treadmill (the Bruce protocol or its modification are the most widely used in the United States) or cycle ergometer (see Chapter 5).

For those unable to perform sufficient physical exertion to adequately complete an exercise ECG test, or when specific clinical conditions exist, pharmacological stress testing with vasodilators or dobutamine is indicated (see Chapter 8). Among patients with resting ECG abnormalities expected to affect repolarization that potentially lead to situations where the ECG response to exercise would be considered non‐diagnostic or falsely positive, imaging with echocardiography or myocardial perfusion imaging (MPI) is indicated. Stress echocardiography is also indicated in specific situations in the assessment of valvular heart disease (see Chapter 7). For selected patients with indwelling permanent cardiac pacemakers, the gradual increase of the atrial paced rate can provide an adequate assessment for myocardial ischemia when combined with a myocardial imaging technique.

The exercise ECG test is used primarily to assess the etiology of chest pain and for detection of CAD. In addition, the exercise ECG test can provide important information about functional capacity (prognosis) and the efficacy of medical and surgical therapy for patients with CAD. Furthermore, an exercise ECG test can be quite useful in assessing the ability of an individual to participate in an exercise program or sport (see Chapters 18 and 19), in the evaluation exercise‐related symptoms, or for assessment of chronotropic competence or exercise‐related arrhythmias.

Myocardial imaging should be performed in combination with the exercise ECG test when false positive or false negative exercise ECG results are anticipated or found and when the exercise ECG test result is equivocal. Due to the infrequent occurrence of ST‐segments shifts with pharmacological stress agents, myocardial imaging is required when pharmacological stress testing is performed (see Chapter 11).

Pathophysiologic Considerations

The exercise stress ECG test has two major purposes:

1. To determine the capability of the coronary circulation to increase oxygen delivery to the myocardium in response to an increased demand. During physical exertion, myocardial oxygen demand is increased by the increase in systolic blood pressure (SBP), contractile state of the heart, and increase of heart rate (HR).
2. To assess the exercise capacity. The major factor determining the exercise capacity is the ability to increase the cardiac output; the product of stroke volume (SV) and HR. In normal individuals, cardiac output (Q) typically increases by a factor of four to sixfold from the resting condition to peak exercise. During moderate to high‐intensity exercise, the further increase in Q is primarily attributable to an increase in HR, as SV generally reaches a plateau at 50–60% of maximal oxygen uptake.

As it is known that the heart already extracts approximately 70% of the oxygen from each unit of blood perfusing the myocardium at rest, oxygen delivery to the myocardium cannot be increased significantly by increasing oxygen extraction. For practical purposes, myocardial metabolism is entirely aerobic, thus coronary blood flow must increase in order to augment the myocardial oxygen supply. In healthy individuals, coronary blood flow is documented to increase in proportion to increased myocardial demand for oxygen.

In response to stress in patients with significant CAD, coronary blood flow fails to adequately increase to meet the increased demand of the myocardium for oxygen, leading to myocardial ischemia. Myocardial ischemia may manifest in a variety of ways during a stress test including anginal pain, ST‐segment and/or T‐wave changes, ventricular dysfunction, various cardiac arrhythmias, or any combination of the preceding.

Physical exercise leads to an increment of myocardial oxygen consumption via the increased HR, intra‐myocardial tension, and contractility. With progressive exercise, coronary blood flow can increase as much as four to sixfold above the basal value. Acceleration of the HR is associated with a linear increment of myocardial oxygen consumption; thus the HR response to an exercise bout provides a useful parameter of myocardial oxygen requirements. By measuring the (systolic) BP during exercise, the product of the HR and BP (“double product” or “rate‐pressure product”) can be derived, which can serve as a practical index of myocardial oxygen uptake.

Preparations and Precautions

As shall be discussed in further detail in Chapter 2, the exercise ECG test requires certain preparations and due consideration of precautions in order to perform the test appropriately and safely. The nature and purpose of the test should be explained in appropriate detail to the patient. All stress tests must be ordered by a licensed independent practitioner. Upon receipt and acceptance of the order by the stress laboratory, the stress test is scheduled as an elective procedure for outpatients as well as for inpatients.

Patients who are to undergo a stress test should be given the following instructions:

• Report for the test either after an overnight fast or three hours following a light meal.
• Routine medications may be taken with small amounts of water.
• Dress in comfortable clothing and wear comfortable walking shoes or sneakers.

Before a patient is to pe...